Science has just published a new analysis of ice core data from Antarctica, covering the last 800,000 years.

In brief, the authors worked on the ice core dating problem (previous attempts at dating each tiny slice of ice had error bars measured in centuries -- way to wide for comfort). With five synchronized independent ice cores now available, and with ice core events now matched to the Laschamp geomagnetic event (41,000 years ago) via the bipolar "seesaw" hypothesis, it is possible to be much more accurate with the dating.

The result still has some residual error, and as before that error increases with the depth of each core. However, it is now possible to resolve the dates of four critical rapid warming events to within a century or so, for both temperatures and carbon dioxide.

Their conclusion: up to the limit of their temporal resolution, the increase in temperature and carbon dioxide are essentially synchronous. There is no resolvable lag of either variable behind the other. The circa 800-year lag of temperature rise behind CO2 rise is not visible in the high-resolution data.

On scales less than a century, the ice core data is silent. Perhaps someday, with many more cores and much better synchronization tools, it may be possible to draw conclusions about which variable causes what kind of change, and on precisely what time scale, but we aren't there yet.

Authors' Abstract:

Understanding the role of atmospheric CO2 during past climate changes requires clear knowledge of how it varies in time relative to temperature. Antarctic ice cores preserve highly resolved records of atmospheric CO2 and Antarctic temperature for the past 800,000 years. Here we propose a revised relative age scale for the concentration of atmospheric CO2 and Antarctic temperature for the last deglacial warming, using data from five Antarctic ice cores. We infer the phasing between CO2 concentration and Antarctic temperature at four times when their trends change abruptly. We find no significant asynchrony between them, indicating that Antarctic temperature did not begin to rise hundreds of years before the concentration of atmospheric CO2, as has been suggested by earlier studies.

Editor's Summary:

Changes in the concentration of atmospheric CO2 and surface air temperature are closely related. However, temperature can influence atmospheric CO2 as well as be influenced by it. Studies of polar ice cores have concluded that temperature increases during periods of rapid warming have preceded increases in CO2 by hundreds of years. Parrenin et al. present a revised age scale for the atmospheric component of Antarctic ice cores, based on the isotopic composition of the N2 that they contain, and suggest that temperature and CO2 changed synchronously over four intervals of rapid warming during the last deglaciation.

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